Similar patients search not working when there's multiple similar results

When registering a new patient, after inputting the new patient name, a list of similar already registered patients should be retrieved and shown on top of the "Register a patient" section.

The issue is that, if more than one similar patient exists, an error occurs on the backend and, no similar patients are retrieved and shown.

No indication of the error is shown to the user, application frontend behaves as if there are no existing similar patients. Error is seen when analysing the browser requests though. 

To reproduce:

1. Open the browser developer console to view the network requests
2. Login to qa-refapp
3. Go to "Register a patient"
4. Input "John" for given name and "S" for family name
5. Click on an empty spot to trigger the onblur of the input
6. No similar results are shown although we already have 3 existing patients with similar name
7. On the developer console we see that, the request to retrieve similar results, returned http 500

When creating a new patient:

Existing patients: